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Friction, Lubrication, and Wear Technology (1997) Part 10

Tham khảo tài liệu 'friction, lubrication, and wear technology (1997) part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Brake Rubbing Speed Effects. Organic brake linings show little variation in their specific wear rate with braking speed when tested from low initial cast iron temperatures. There typically is a slight rise of wear rate below a rubbing speed of 2 m s 6.5 ft s . Brake asperity flash temperatures are known to vary primarily with speed as has been described by Blok Ref 2 and more recently by Lim and Ashby Ref 3 . Above 1 m s 3.3 ft s asperity temperatures appear to range from 1000 to 1100 C 1830 to 2010 F . It is presumed that the variation of lining wear rate and the associated variation of friction level are related to this flash temperature transition. At very high rubbing speeds the lining wear rate increases. This increase is greater when the initial brake drum or disk temperature is high. It is presumed that this speed effect is simply the result of higher interfacial temperatures. Model wear data presented later support this presumption. Semimet friction materials also exhibit unique behavior with speed. At rubbing speeds below 2 m s 6.5 ft s semimet lining wear rates also increase but to a significantly greater extent than do the organic linings. Thereafter the semimet brake linings provide a nearly constant specific wear rate with rubbing speed until a transition condition is reached. Higher speeds then generate much higher lining wear rates to 100 times or more . During full brake dynamometer testing of semimet brake linings it was found that four brake stops from 160 km h 100 mph produced as much lining wear as over 500 brake stops from 50 65 100 and 130 km h 30 40 60 and 80 mph . There are differences among commercial semimet brake lining formulations in terms of rubbing speed transition values. Higher transition speeds were found with a semimet lining that contained a small amount of para-aramid pulp. It is conjectured that this high-strength thermoplastic material provided enhanced near-surface brake lining strength and helped to prevent friction welding